Increasing atmospheric CO 2 stimulates photosynthesis which can increase net primary production (NPP), but at longer timescales may not necessarily increase plant biomass. Here we analyse the four decade-long CO 2 -enrichment experiments in woody ecosystems that measured total NPP and biomass. CO 2 enrichment increased biomass increment by 1.05 ± 0.26 kg C m −2 over a full decade, a 29.1 ± 11.7% stimulation of biomass gain in these early-secondary-succession temperate ecosystems. This response is predictable by combining the CO 2 response of NPP (0.16 ± 0.03 kg C m −2 y −1 ) and the CO 2 -independent, linear slope between biomass increment and cumulative NPP (0.55 ± 0.17). An ensemble of terrestrial ecosystem models fail to predict both terms correctly. Allocation to wood was a driver of across-site, and across-model, response variability and together with CO 2 -independence of biomass retention highlights the value of understanding drivers of wood allocation under ambient conditions to correctly interpret and predict CO 2 responses.
Bibliographical noteFunding Information:
The FACE Model-Data Synthesis project was supported by the US Department of Energy, Office of Science Biological and Environmental Research program. Oak Ridge National Laboratory is operated by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy. M.D.K. also acknowledges support from the ARC Centre of Excellence for Climate Extremes (CE170100023). Support for J.P.M. and M.L. was provided by a DOE-TES program grant DE-SC0008339 and the Smith-sonian Institution. A.K.J. and S.S. were supported by the US National Science Foundation (NSF-AGS-12-43071). R.O. was supported by the Erkko Visiting Professor Programme of the Jane and Aatos Erkko 375th Anniversary Fund through the University of Helsinki.
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